1. Field of the Invention
The present invention relates to a solid state laser generation apparatus, and relates in particular to a technology for improving the generation efficiency by decreasing the distance of separation, or spacing, between the components such as lasing rods and other peripheral devices.
2. Background Art
In rod type solid state lasers such as Nd.multidot.YAG lasers, the output power is increased by providing a number of laser generation rods 3 (hereinafter referred to as the rods 3) arranged in a cascading manner as shown in FIG. 9, on a common optical axis B between a rear reflecting mirror 1 opposing an output reflecting mirror 2 disposed at a distance.
Also, a suitable number of excitation lamps 4, such as arc lamps acting as a laser beam generation source, are disposed on the side of the rod 3, as shown in FIG. 10. Around the excitation lamps 4, there is disposed a reflecting cylinder 5, which reflects and focuses the excitation beams onto the rod 3. In FIG. 10, 6 is a rod holder, 7 is an electrode and 8 is a lamp holder.
By irradiating each of the several rods 3 with the excitation radiation, and by having the generated laser beams reflect back and forth between the mirrors, a pumped excited state is generated.
In such a laser generation apparatus, the rods 3 are heated by the excitation energy, and as the temperature rises, such effects as differential thermal expansion and changes in the index of refraction caused by internal stresses cause a phenomenon known as the thermal lens effect (referred to as thermal effect hereinbelow) which produce optical effects similar to a convex lens which produces converging beams.
Because of such converging effects of the reflecting beams, the parallel alignment between the beam paths in the rods 3 and the optical axis B is degraded, resulting in a tendency for the lasing volume to decrease, which is the internal volume contributing to the generation of laser beams within the rods 3, and consequently the lasing efficiency of the overall apparatus is lowered.
Conventional remedial method is to compensate for the thermal degradation effects by fabricating the end surfaces 3a of the rods 3 in a concave shape so as to produce a refraction radius of -2 m to -1 m in the case of a laser rod of 152 mm length and 8 mm diameter, for example.
However, in the case of the conventional laser apparatus shown in FIG. 10, during the initial generation phase of the laser, the temperature of the rods 3 has not yet risen to the region which produces the thermal effect. The concave end surface effects (termed concave end effect) are operative, however, and the generated laser beams are apt to be diverged away during the early phases, thus requiring a larger initial energy input to bring the apparatus to the lasing stage. The lasing threshold value is thus raised, and this is a reason for impairing the lasing initiation ability.
To improve the lasing initiation ability and increase the lasing efficiency, it is effective to arrange the rods 3 so that the distance LR, in FIG. 9, between the rods 3 is less than the distance L1 and L2 between the rods and the mirrors. However, to provide such an arrangement, it is necessary to decrease the lengths of the portion of the rod holder 6 and the lamp holder 8, which extend beyond the ends of the rod laser. There is some possibility for decreasing the extended length of the rod holder 6, but the lamp holder 8 is more difficult to shorten because its length is governed by the length of the electrode.
The objectives of the present invention are therefore to:
1. increase the lasing initiation ability by reducing the threshold value of the excitation energy needed for the initiation of lasing action; PA1 2. to raise the overall lasing efficiency; PA1 3. to enable high laser power output easily and PA1 4. to make the entire apparatus to become compact. PA1 (a) laser beam generating means for generating laser beams aligned on said optical axis; PA1 (b) a plurality of excitation means for providing excitation energy to said laser generation means, said excitation means being disposed parallel to said laser generation means, aligned on a common optical path and having electrode terminal means; PA1 (c) end holding means for retaining the ends of said laser beam generating means; and PA1 (d) terminal holding means for retaining the ends including electrode terminal means, of said plurality of excitation means;